Method and apparatus for reducing transmission errors caused by periodic transients in digital subscriber line (DSL) communication systems

ABSTRACT

A transient pre-emptor includes a processor configured to detect transients in a communications system. After the processor detects a transient in the communications system, it causes a data communications equipment to suspend or reduce data transmission during the occurrence of a subsequent transient.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 09/638,924,filed Oct. 15, 2000, which claims the benefit of U.S. ProvisionalApplication No. 60/161,741, filed Oct. 27, 1999, and which is also acontinuation of application Ser. No. 09/395,020. Application Ser. Nos.09/638,924, 60/161,741 and 09/395,020 are each incorporated byreference.

TECHNICAL FIELD

The present invention generally relates to communication systems and,more particularly, to a method and apparatus for reducing transmissionerrors caused by periodic transients in digital subscriber line (DSL)communication systems.

BACKGROUND OF THE INVENTION

In networks that utilize copper pairs, also referred to as metallicloops or twisted wire pairs, baseband telephony services and DSLservices are often provided over the same copper pair. In these types ofnetworks, transients associated with baseband ringing used to signalincoming call requests can result in the occurrence of bit errors indata being transmitted with DSL technology. Most if not all DSL systemsare susceptible to such transients.

Plain old telephone service (POTS) filters or splitters are widely usedto separate the baseband telephony services, which occupy lowerfrequencies (i.e., typically below about 4 kilohertz (kHz)), from thehigher data frequencies associated with DSL services. POTS filtersnormally filter out signals above about 20 kHz so that noise in thebaseband does not adversely affect the DSL transmissions. However, evenwhere POTS filters are utilized, it has been determined that periodictransients are sufficiently powerful to couple from adjacent wiresresulting in impulse noise and bit errors in data being transmitted atthe higher DSL data rates. DSL communications equipment may also employpowerful block codes and interleavers to disperse the transient. Thesemethods have undesirable complexity and result in significantly slowerdata transmission rates. Accordingly, a need exists for a method and

SUMMARY OF THE INVENTION

The present invention provides an apparatus and method for reducingtransmission errors in a communications system. The apparatus, atransient pre-emptor, comprises a processor configured to detecttransients. After the processor detects a transient in thecommunications system, it causes communications equipment to suspend orreduce data transmission during the occurrence of a subsequenttransient.

The present invention can also be viewed as providing a method forreducing transmission errors. In this regard, the method can be broadlysummarized by the following steps: detecting a transient in thecommunications system and suspending or reducing the data transmissionrate between data communications equipment during the occurrence of asubsequent transient.

Other systems, methods, features, and advantages of the presentinvention will be or become apparent to one with skill in the art uponexamination of the following drawings and detailed description. It isintended that all such additional systems, methods, features, andadvantages be included within this description, be within the scope ofthe present invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a network that utilizes a copper pair forcommunicating baseband telephony services and DSL data services betweena central office and a subscriber, or customer, premises.

FIG. 2 is a functional block diagram of a transient pre-emptor inaccordance with the preferred embodiment of the present invention.

FIG. 3 is a flow chart of a data collection routine executed by thetransient pre-emptor shown in FIG. 2 to collect data about periodictransients.

FIG. 4 is a flow chart of a transient pre-emption routine executed bythe transient pre-emptor shown in FIG. 2 to alleviate periodic transientphenomena.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a communications network 5 utilized for communicatingbaseband telephony services and DSL services over a copper pair 16. Thenetwork 5 comprises a central office (CO) 9, which is coupled by acopper pair 16 (also known as a subscriber loop) to a customer premises(CP) 8. The network 5 may be, for example, but not limited to, part ofthe public switched telephone network (PSTN). The CO 9 comprises a datacommunications equipment (DCE) 15 that is electrically coupled via thecopper pair 16 to a DCE 6 located at the CP 8. The DCE 6 located at theCP 8 is in communication with a data terminal equipment (DTE) device 7,which may be, for example, but not limited to, a personal computer, aworkstation, a minicomputer, or a mainframe computer.

For ease of illustration, only one CP 8 is shown in FIG. 1. Typically,many CPs 8 will be electrically coupled to the CO 9 by the copper pair16. Also, the CO 9 normally comprises many DCEs 15 for communicatingwith many subscribers. For ease of illustration, only one of the DCEslocated at the CO 9 is shown in FIG. 1. Also, it should be noted thatthe DCE 15 located at the CO 9 typically communicates via copper pair 16with multiple customer premises DCEs. In order to clearly demonstratethe concepts of the present invention, the present invention will bediscussed with reference to communication between a single DCE 15located at the CO 9 and a single DCE 6 located at the CP 8. Thoseskilled in the art will understand the manner in which multipleinstances of the transient pre-emptor may be implemented in a networksuch as that shown in FIG. 1.

In accordance with the preferred embodiment of the present invention,the transient pre-emptor 10 is situated in the DCE 15 located in the CO9. The transient pre-emptor 10 is capable of detecting transients on thecopper pair and of causing the rate(s) of data transmission to bereduced to a predetermined rate upon detecting transients. Thispredetermined rate of data transmission is utilized by both the DCE 15located at the CO 9 and by the DCE 6 located at the CP 8. Therefore,preferably the transient pre-emptor 10 is incorporated into the DCE 15located at the CO 9 since the DCE 15 typically is provided with thecapability of commanding the customer premises DCE to adjust its rate(s)of data transmission.

However, those skilled in the art will understand that the DCE 6 locatedat the CP 8 could be configured to adjust its own rate(s) of datatransmission upon detecting transients. The customer premises DCE 6could also be configured to send a command to the DCE 15 located at theCO 9 that would cause the DCE 15 located at the CO 9 to adjust itsrate(s) of data transmission. Therefore, it will be understood that thepresent invention is not limited with respect to the location at whichthe transient pre-emptor 10 is physically implemented.

FIG. 2 is a functional block diagram of the transient pre-emptor 10 ofthe present invention in accordance with the preferred embodiment. Thetransient pre-emptor 10 of the present invention preferably comprises alow-pass filter 11, an analog to digital converter 12, a processor 13,and memory 14. The processor 13 is preferably a digital signalprocessor, but may also be a general purpose processor, a specificpurpose processor, or a hardware component capable of executinginstructions or performing electronic computations. The processor 13 isalso preferably the CPU of the DCE 15 located at the CO 9. However, aseparate processor may be utilized for performing the method of thepresent invention, as will be understood by those skilled in the art.Memory 14 may include volatile and/or non-volatile memory and maycomprise one or more components selected from a wide variety of memoryhardware such as, for example, RAM, ROM, or a combination thereof.

The low-pass filter 11 separates telephony baseband signals from DSLsignals and passes the telephony baseband signals to ananalog-to-digital converter (ADC) 12. The baseband telephony signalsnormally have a frequency that is below 4 kilohertz. The basebandringing wave form is an analog waveform that is within this frequencyrange, but is at a much higher voltage level than the voltage levels ofother baseband telephony signals being transmitted over the network,including the on-hook and off-hook voltage levels.

Typically, the baseband ringing waveform that causes the transients hasa voltage level that is approximately 200 volts peak-to-peak and hasshort-duration rise and fall time. The ADC 12 receives this waveform andconverts it into digital signals, which are then delivered to theprocessor 13. The processor 13 monitors the digital signals receivedfrom the ADC 12 to determine whether the a digital signal corresponds toa transient. A digital signal corresponds to a transient if it has ashort duration rise or fall time and covers a sufficiently wide range ofvalues. If the processor detects a transient, it stores informationabout its timing, duration and magnitude in memory 14.

It should be noted that there are a variety of known ways to detecttransients. The present invention is not limited with respect to themanner in which this is accomplished. Preferably, transients aredetected in the manner discussed above by utilizing the low-pass filter11, the ADC 12 and the processor 13 in the aforementioned manner.However, those skilled in the art will understand that this may beaccomplished by utilizing other techniques and devices.

FIG. 3 is a flow chart of a data collection routine executed by thetransient pre-emptor 10 (shown in FIG. 2) to collect data about periodictransients. After an initial transient is detected at block 31, theprocessor 13 (FIG. 2) determines whether enough information aboutperiodic transients had been previously collected and stored in memory14. If so, the processor 13 (FIG. 2) executes the routine 40 shown inFIG. 4, and discussed in more detail below. Otherwise, the processor 13suspends or reduces data transmission, as indicated in block 33, betweenthe DCE 15 located at the CO 9 and the DCE 6 located at the CP 8 (FIG.1). The preferred course of action is to cease transmission until enoughdata about the periodic transients are collected. However, if thedisturbance caused by the initial transient is minor, then the datatransmission rate may be reduced to the highest possible rate that willbe immune to further transients of similar intensity.

A suspension or reduction in data transmission is preferably achieved ina two step process—first the downstream data transmission rate isadjusted and then the upstream data transmission rate is adjusted. Oncethe data transmission rates are appropriately modified, subsequenttransients are monitored as indicated in block 34. The processor 13monitors transient by measuring the duration, magnitude and cadence oftransients over a predetermined length of time that is calculated tospan the occurrence of several transients. Measurements made by theprocessor 13 are stored in memory 14 (FIG. 2). When the predeterminedlength of time expires, transmission rates are restored to theiroriginal values as indicated by block 35. The restoration of theoriginal transmission rates is preferably achieved in a two stepprocess—first the downstream data transmission rate is restored and thenthe upstream data transmission is restored.

The processor 13 (FIG. 2) then processes the data stored in memory 14 todetermine if enough data has been collected on transients (block 36). Ifenough data has been collected then, as indicated in block 37, theprocessor 13 calculates the timing of the periodic transmission rateadjustments that will be made in anticipation of future transients, andthen executes the routine 40 that will be discussed in more detailbelow. Otherwise, if not enough data has been collected, the processor13 determines, as indicated in block 38, based on the cadence of thetransients and the number of transients detected, whether anothertransient is expected. If another transient is expected, then processor13 re-executes the steps indicated in blocks 33, 34, 35, and 36 asdescribed above. If no further transients are expected as part of theseries of periodic transients measured according to block 34, then theroutine 30 terminates and returns to the point of execution from whichit was called, as indicated by block 39.

FIG. 4 is a flow chart of a transient pre-emption routine executed bythe present invention shown in FIG. 2 to alleviate periodic transientphenomena. As indicated in block 42, the processor 13 (FIG. 2) suspendsor reduces data transmission between the DCE 15 and the DCE 6 at acalculated time before the next transient is expected. The time that asubsequent transient is expected to occur can be determined by theprocessor 13 from the information gathered from executing the routineshown in FIG. 3 and stored in memory 14 (FIG. 2).

The calculated time when transmission is to be suspended or reduceddepends on several factors. These factors include: the variability ofthe cadence intervals of the transients, the time that it takes totransmit a pending message, the maximum time that it takes to receivethe longest response message, and the time it takes to transmit ratereduction commands. These factors can be stored in memory 14 (FIG. 2)and used by the processor 13 to help determine when transmission is tobe suspended or reduced. As a non-limiting example, in onecommunications system, it was determined that suspending transmissionand polling by the DCE 15 (FIG. 1) about 50 msec before the nextexpected transient produced the best results. It should be noted thatthe optimal time period also depends on the accuracy of the cadencemeasurement, and on the transient response of the system filters andwill therefore vary among communications systems. A suspension orreduction in data transmission is preferably achieved in a two stepprocess—first the downstream data transmission rate is adjusted and thenthe upstream data transmission rate is adjusted. The preferred course ofaction is to suspend transmission during transients. However, if thetransients are not too severe, then the data rate may be reduced to thehighest possible rate that will be immune to additional transients ofsimilar intensity.

After data transmission is reduced or suspended, it is restored at acalculated time after the subsequent transient is expected to haveoccurred, as indicated in block 44. The time that a subsequent transientis expected to have occurred can be determined by the processor 13 (FIG.2) from the cadence information gathered by executing the routine shownin FIG. 3 and stored in memory 14 (FIG. 2). As a non-limiting example,in one communications system, it was determined that resuming polling 3msec after the transient was expected to have occurred helped achievethe best performance. The optimal time period, however, depends on thevariability of the transient cadence interval, on the accuracy of thecadence measurement, and on the transient response of the systemfilters, and will therefore vary among communication systems. Ingeneral, the longer the time period during which transmission is reducedor suspended, the greater the probability of alleviating disturbancescaused by a transient.

As an alternative approach to the step in block 44, the processor 13(FIG. 2) would cause transmission to be restored only after a subsequenttransient is detected or after failing to detect a subsequent transientfor a predetermined period of time. This alternative approach ensuresthat variability in the cadence or in the measurements thereof will notresult in transmission being restored prior to the occurrence of theanticipated transient. In addition, by continuing to measure the timing,duration, and cadence of transients, the process can be tuned to betterpredict and alleviate subsequent transients. The tuning can be achieved,for example, by revising the estimated time between transients.

The restoration of the original data rates is preferably achieved in atwo step process—first, the downstream data transmission rate isrestored and then the upstream data transmission rate is restored. Afterthe transmission rates are restored to their original values, theprocessor 13 (FIG. 2) determines if, as indicated in block 46, atransient was detected during the time that the transmission wassuspended or reduced. If the processor 13 determines that a transientwas detected, then the processor 13 re-executes the steps indicated inblocks 42, 44, and 46 as explained above in order to protect againstadditional transients. These steps would continue to be executed as longas additional transients continue to be detected. If no furthertransients are detected for a predetermined period of time, then theroutine 40 terminates and returns to the point of execution from whichit was called, as indicated by block 48.

Any process descriptions or blocks in flow charts should be understoodas representing modules, segments, or portions of code which include oneor more executable instructions for implementing specific logicalfunctions or steps in the process, and alternate implementations areincluded within the scope of the preferred embodiment of the presentinvention in which functions may be executed out of order from thatshown or discussed, including substantially concurrently or in reverseorder, depending on the functionality involved, as would be understoodby those reasonably skilled in the art of the present invention.

Routines 30 & 40 can be implemented in a computer program which comprisean ordered listing of executable instructions for implementing logicalfunctions. Such a program can be embodied in any computer-readablemedium for use by or in connection with an instruction execution system,apparatus, or device, such as a computer-based system,processor-containing system, or other system that can fetch theinstructions from the instruction execution system, apparatus, or deviceand execute the instructions. In the context of this document, a“computer-readable medium” can be any means that can contain, store,communicate, propagate, or transport the program for use by or inconnection with the instruction execution system, apparatus, or device.The computer readable medium can be, for example but not limited to, anelectronic, magnetic, optical, electromagnetic, infrared, orsemiconductor system, apparatus, device, or propagation medium. Morespecific examples (a nonexhaustive list) of the computer-readable mediumwould include the following: an electrical connection (electronic)having one or more wires, a portable computer diskette (magnetic), arandom access memory (RAM) (electronic), a read-only memory (ROM)(electronic), an erasable programmable read-only memory (EPROM or Flashmemory) (electronic), an optical fiber (optical), and a portable compactdisc read-only memory (CDROM) (optical). Note that the computer-readablemedium could even be paper or another suitable medium upon which theprogram is printed, as the program can be electronically captured, viafor instance optical scanning of the paper or other medium, thencompiled, interpreted or otherwise processed in a suitable manner ifnecessary, and then stored in a computer memory.

The apparatus and/or method of reducing transmission errors of thepresent invention can be implemented in hardware, software, firmware, ora combination thereof. In the preferred embodiment(s), the method ofreducing transmission errors is implemented in software or firmware thatis stored in a memory and that is executed by a suitable instructionexecution system. If implemented in hardware, as in an alternativeembodiment, the method of reducing transmission errors can implementedwith any or a combination of the following technologies, which are allwell known in the art: a discrete logic circuit(s) having logic gatesfor implementing logic functions upon data signals, an applicationspecific integrated circuit (ASIC) having appropriate combinationallogic gates, a programmable gate array(s) (PGA), a field programmablegate array (FPGA), etc.

It should be emphasized that the above-described embodiments of thepresent invention, are merely possible examples of the implementations,merely setting forth for a clear understanding of the principles of theinventions. Many variations and modifications may be made to theabove-described embodiments of the invention without departingsubstantially from the spirit of the principles of the invention. Allsuch modifications and variations are intended to be included hereinwithin the scope of the disclosure and present invention and protectedby the following claims.

1. A method for reducing transmission errors in a data communicationsequipment, the method comprising the steps of: collecting datadescribing a transient; determining a rate adjustment time based on thecollected data; and adjusting, at the rate adjustment time, atransmission rate associated with the data communications equipment. 2.The method of claim 1, further comprising the steps of: determining,based on the collected data, an expected occurrence time of a subsequenttransient start; and reducing, at the expected occurrence time of thesubsequent transient start, the transmission rate from a first value. 3.The method of claim 2, further comprising the steps of: determining,based on the collected data, an expected occurrence time of a subsequenttransient end; and restoring, at the expected occurrence time of thesubsequent transient end, the transmission rate to the first value. 4.The method of claim 1, further comprising the step of detecting thetransient, and wherein the collecting step is responsive to thedetecting step.
 5. The method of claim 4, further comprising the stepof: responsive to the detecting, reducing the transmission rate from afirst value.
 6. The method of claim 5, wherein the reducing step reducesthe transmission rate to zero.
 7. The method of claim 5, furthercomprising the step of: restoring the transmission rate to the firstvalue.
 8. The method of claim 1, wherein the collecting data step occursover a predetermined length of time.
 9. The system of claim 1, whereinthe collected data comprises at least one of transient duration,transient magnitude, and transient cadence.
 10. A computer-readablemedium having a program for reducing transmission errors in a datacommunications equipment having a current transmission rate, the programcomprising the steps of: collecting data describing a transient;determining a rate adjustment time based on the collected data; andadjusting, at the rate adjustment time, a transmission rate associatedwith the data communications equipment.
 11. The computer-readable mediumof claim 10, the program further comprising the steps of: determining,based on the collected data, an expected occurrence time of a subsequenttransient start; and reducing, at the expected occurrence time of thesubsequent transient start, the transmission rate from a first value.12. The computer-readable medium of claim 11, the program furthercomprising the steps of: determining, based on the collected data, anexpected occurrence time of a subsequent transient end; and restoring,at the expected occurrence time of the subsequent transient end, thetransmission rate to the first value.
 13. The computer-readable mediumof claim 10, the program further comprising the steps of: detecting thetransient; and responsive to the detecting, reducing the transmissionrate of the data communications equipment from a first value.
 14. Thecomputer-readable medium of claim 13, the program further comprising thestep of: restoring the transmission rate to the first value.
 15. Thecomputer-readable medium of claim 10, wherein the collected datacomprises at least one of transient duration, transient magnitude, andtransient cadence.
 16. A system for reducing transmission errors in adata communications equipment having a current transmission rate, thesystem comprising the steps of: means for collecting data describing atransient; means for determining, based on the collected data, a rateadjustment time; and means for adjusting, at the rate adjustment time, atransmission rate associated with the data communications equipment. 17.The system of claim 16, further comprising: means for determining, basedon the collected data, an expected occurrence time of a subsequenttransient start; and means for reducing, at the expected occurrence timeof the subsequent transient start, the transmission rate from a firstvalue.
 18. The system of claim 17, further comprising: means fordetermining, based on the collected data, an expected occurrence time ofa subsequent transient end; and means for restoring, at the expectedoccurrence time of the subsequent transient end, the transmission rateto the first value.
 19. The system of claim 16, further comprising:means for detecting the transient; and means for reducing thetransmission rate from a first value, wherein the means for reducing isresponsive to the means detecting.
 20. The system of claim 19, furthercomprising means for restoring the current transmission rate to thefirst transmission rate.